Slade Green to Chessington South fare routing

I noticed for a forthcoming trip that the PAYG fare from Slade Green to Chessington included a £3.50 off peak journey.

I can only see two potential ways of getting this fare as it clearly avoids the normal way of travelling by changing at Waterloo (made more difficult now by the lack of direct trains to Charing Cross)

These are Slade Green to Abbey Wood then swapping to the Elizabeth Line to Whitechapel.
Overground from here to Clapham Junction and picking up the national rail service to Chessington South.

The other being travelling from Slade Green to New Cross and picking up the Overground from there to Clapham Junction and again national rail to Chessington South.

Are both routes valid for the £3.50 off peak fare?
Are you aware of any pink validators on these routes that I’d need to tap ?
Is there enough time to complete the trip within the max journey time or is it likely to be touch and go?

Thank you for your help 🙂